Fig. 1.

Signaling pathways involving Bruton’s tyrosine kinase (BTK). BTK is placed within the pathways of the B cell receptor (BCR), the Fc receptor (FcR), as well as in the Toll-like receptor (TLR) and chemokine receptor cascades. It has a central place in relaying extracellular signaling to downstream pathways such as the nuclear factor “kappa-light-chain-enhancer” of activated B cells (NFkB), nuclear factor of activated T cells (NFAT), protein kinase C (PKC), and mitogen-activated protein kinase (MAPK) cascades. Solid arrows correspond to strong, direct involvement of BTK whereas dotted arrows indicate a weaker involvement. ITAM immunoreceptor tyrosine-based activation motif